Autoimmune diabetes results from the loss of self-tolerance to pancreatic islet Ag that ultimately leads to inflammatory destruction of insulin-producing beta cells. A growing body of data indicate that unique immunoregulatory CD4 subsets that in some instances are associated with cytokine profiles that distinguish them from Th1 or Th2 cells, control CD4 cell homeostasis and are actively involved in maintaining self-tolerance. It is not yet clear whether different subsets of regulatory cells can function at the induction and effector phases of an autoimmune response. Recent studies indicate that such T cells may be key to the prevention of several organ-specific autoimmune diseases and that diabetes onset may be precipitated when regulatory CD4 cells are overwhelmed by autoaggressive Th1 effector populations. Identifying means to induce such regulatory populations and understanding the mechanisms by which they function to either prohibit activation of autoaggressive CD4 cells or control their responses will enhance our understanding of immune regulation and may yield new insights into immunotherapeutic approaches for treatment of IDDM. We have developed an adoptive transfer model to study regulation of IDDM by CD4 subsets. We find that Thl cells but not Th2 cells that are generated from islet-specific BDC2.5 transgenic CD4 cells cause rapid onset of IDDM in both NOD.scid and NOD recipients. Although Th2 cytokines are associated with protection from IDDM, Th2 cells cannot reproducibly inhibit or delay disease onset in our model to any significant extent. However, we have recently found that TGF-beta1 induces a population of BDC CD4 cells with a cytokine and chemokine secretion pattern typical of Th1 cells, but which can function in IDDM as a regulatory population with the capacity to inhibit Th1-mediated disease in NOD.scid mice and the spontaneous development of IDDM in NOD mice. The aims of the proposed studies are to 1) identify the precursor population(s) that give rise to TR cells and parameters that regulate their development; 2) investigate their in vivo localization and response, turnover, and requirements for Ag for in vivo persistence, and 3) to investigate mechanism(s) by which regulatory cells control the effector phase of Th1-mediated IDDM. From these studies we hope to determine if induction and expansion of regulatory CD4 cells in vitro offers potential for clinical treatment of IDDM.